michael@0: /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
michael@0: /* vim: set ts=2 sw=2 et tw=80: */
michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: #include "WheelHandlingHelper.h"
michael@0: 
michael@0: #include "mozilla/EventDispatcher.h"
michael@0: #include "mozilla/EventStateManager.h"
michael@0: #include "mozilla/MouseEvents.h"
michael@0: #include "mozilla/Preferences.h"
michael@0: #include "nsCOMPtr.h"
michael@0: #include "nsContentUtils.h"
michael@0: #include "nsIContent.h"
michael@0: #include "nsIDocument.h"
michael@0: #include "nsIPresShell.h"
michael@0: #include "nsIScrollableFrame.h"
michael@0: #include "nsITimer.h"
michael@0: #include "nsPresContext.h"
michael@0: #include "prtime.h"
michael@0: #include "Units.h"
michael@0: 
michael@0: namespace mozilla {
michael@0: 
michael@0: /******************************************************************/
michael@0: /* mozilla::DeltaValues                                           */
michael@0: /******************************************************************/
michael@0: 
michael@0: DeltaValues::DeltaValues(WidgetWheelEvent* aEvent)
michael@0:   : deltaX(aEvent->deltaX)
michael@0:   , deltaY(aEvent->deltaY)
michael@0: {
michael@0: }
michael@0: 
michael@0: /******************************************************************/
michael@0: /* mozilla::WheelHandlingUtils                                    */
michael@0: /******************************************************************/
michael@0: 
michael@0: /* static */ bool
michael@0: WheelHandlingUtils::CanScrollInRange(nscoord aMin, nscoord aValue, nscoord aMax,
michael@0:                                      double aDirection)
michael@0: {
michael@0:   return aDirection > 0.0 ? aValue < static_cast<double>(aMax) :
michael@0:                             static_cast<double>(aMin) < aValue;
michael@0: }
michael@0: 
michael@0: /* static */ bool
michael@0: WheelHandlingUtils::CanScrollOn(nsIScrollableFrame* aScrollFrame,
michael@0:                                 double aDirectionX, double aDirectionY)
michael@0: {
michael@0:   MOZ_ASSERT(aScrollFrame);
michael@0:   NS_ASSERTION(aDirectionX || aDirectionY,
michael@0:                "One of the delta values must be non-zero at least");
michael@0: 
michael@0:   nsPoint scrollPt = aScrollFrame->GetScrollPosition();
michael@0:   nsRect scrollRange = aScrollFrame->GetScrollRange();
michael@0:   uint32_t directions = aScrollFrame->GetPerceivedScrollingDirections();
michael@0: 
michael@0:   return (aDirectionX && (directions & nsIScrollableFrame::HORIZONTAL) &&
michael@0:           CanScrollInRange(scrollRange.x, scrollPt.x,
michael@0:                            scrollRange.XMost(), aDirectionX)) ||
michael@0:          (aDirectionY && (directions & nsIScrollableFrame::VERTICAL) &&
michael@0:           CanScrollInRange(scrollRange.y, scrollPt.y,
michael@0:                            scrollRange.YMost(), aDirectionY));
michael@0: }
michael@0: 
michael@0: /******************************************************************/
michael@0: /* mozilla::WheelTransaction                                      */
michael@0: /******************************************************************/
michael@0: 
michael@0: nsWeakFrame WheelTransaction::sTargetFrame(nullptr);
michael@0: uint32_t WheelTransaction::sTime = 0;
michael@0: uint32_t WheelTransaction::sMouseMoved = 0;
michael@0: nsITimer* WheelTransaction::sTimer = nullptr;
michael@0: int32_t WheelTransaction::sScrollSeriesCounter = 0;
michael@0: bool WheelTransaction::sOwnScrollbars = false;
michael@0: 
michael@0: /* static */ bool
michael@0: WheelTransaction::OutOfTime(uint32_t aBaseTime, uint32_t aThreshold)
michael@0: {
michael@0:   uint32_t now = PR_IntervalToMilliseconds(PR_IntervalNow());
michael@0:   return (now - aBaseTime > aThreshold);
michael@0: }
michael@0: 
michael@0: /* static */ void
michael@0: WheelTransaction::OwnScrollbars(bool aOwn)
michael@0: {
michael@0:   sOwnScrollbars = aOwn;
michael@0: }
michael@0: 
michael@0: /* static */ void
michael@0: WheelTransaction::BeginTransaction(nsIFrame* aTargetFrame,
michael@0:                                    WidgetWheelEvent* aEvent)
michael@0: {
michael@0:   NS_ASSERTION(!sTargetFrame, "previous transaction is not finished!");
michael@0:   MOZ_ASSERT(aEvent->message == NS_WHEEL_WHEEL,
michael@0:              "Transaction must be started with a wheel event");
michael@0:   ScrollbarsForWheel::OwnWheelTransaction(false);
michael@0:   sTargetFrame = aTargetFrame;
michael@0:   sScrollSeriesCounter = 0;
michael@0:   if (!UpdateTransaction(aEvent)) {
michael@0:     NS_ERROR("BeginTransaction is called even cannot scroll the frame");
michael@0:     EndTransaction();
michael@0:   }
michael@0: }
michael@0: 
michael@0: /* static */ bool
michael@0: WheelTransaction::UpdateTransaction(WidgetWheelEvent* aEvent)
michael@0: {
michael@0:   nsIScrollableFrame* sf = GetTargetFrame()->GetScrollTargetFrame();
michael@0:   NS_ENSURE_TRUE(sf, false);
michael@0: 
michael@0:   if (!WheelHandlingUtils::CanScrollOn(sf, aEvent->deltaX, aEvent->deltaY)) {
michael@0:     OnFailToScrollTarget();
michael@0:     // We should not modify the transaction state when the view will not be
michael@0:     // scrolled actually.
michael@0:     return false;
michael@0:   }
michael@0: 
michael@0:   SetTimeout();
michael@0: 
michael@0:   if (sScrollSeriesCounter != 0 && OutOfTime(sTime, kScrollSeriesTimeout)) {
michael@0:     sScrollSeriesCounter = 0;
michael@0:   }
michael@0:   sScrollSeriesCounter++;
michael@0: 
michael@0:   // We should use current time instead of WidgetEvent.time.
michael@0:   // 1. Some events doesn't have the correct creation time.
michael@0:   // 2. If the computer runs slowly by other processes eating the CPU resource,
michael@0:   //    the event creation time doesn't keep real time.
michael@0:   sTime = PR_IntervalToMilliseconds(PR_IntervalNow());
michael@0:   sMouseMoved = 0;
michael@0:   return true;
michael@0: }
michael@0: 
michael@0: /* static */ void
michael@0: WheelTransaction::MayEndTransaction()
michael@0: {
michael@0:   if (!sOwnScrollbars && ScrollbarsForWheel::IsActive()) {
michael@0:     ScrollbarsForWheel::OwnWheelTransaction(true);
michael@0:   } else {
michael@0:     EndTransaction();
michael@0:   }
michael@0: }
michael@0: 
michael@0: /* static */ void
michael@0: WheelTransaction::EndTransaction()
michael@0: {
michael@0:   if (sTimer) {
michael@0:     sTimer->Cancel();
michael@0:   }
michael@0:   sTargetFrame = nullptr;
michael@0:   sScrollSeriesCounter = 0;
michael@0:   if (sOwnScrollbars) {
michael@0:     sOwnScrollbars = false;
michael@0:     ScrollbarsForWheel::OwnWheelTransaction(false);
michael@0:     ScrollbarsForWheel::Inactivate();
michael@0:   }
michael@0: }
michael@0: 
michael@0: /* static */ void
michael@0: WheelTransaction::OnEvent(WidgetEvent* aEvent)
michael@0: {
michael@0:   if (!sTargetFrame) {
michael@0:     return;
michael@0:   }
michael@0: 
michael@0:   if (OutOfTime(sTime, GetTimeoutTime())) {
michael@0:     // Even if the scroll event which is handled after timeout, but onTimeout
michael@0:     // was not fired by timer, then the scroll event will scroll old frame,
michael@0:     // therefore, we should call OnTimeout here and ensure to finish the old
michael@0:     // transaction.
michael@0:     OnTimeout(nullptr, nullptr);
michael@0:     return;
michael@0:   }
michael@0: 
michael@0:   switch (aEvent->message) {
michael@0:     case NS_WHEEL_WHEEL:
michael@0:       if (sMouseMoved != 0 &&
michael@0:           OutOfTime(sMouseMoved, GetIgnoreMoveDelayTime())) {
michael@0:         // Terminate the current mousewheel transaction if the mouse moved more
michael@0:         // than ignoremovedelay milliseconds ago
michael@0:         EndTransaction();
michael@0:       }
michael@0:       return;
michael@0:     case NS_MOUSE_MOVE:
michael@0:     case NS_DRAGDROP_OVER: {
michael@0:       WidgetMouseEvent* mouseEvent = aEvent->AsMouseEvent();
michael@0:       if (mouseEvent->IsReal()) {
michael@0:         // If the cursor is moving to be outside the frame,
michael@0:         // terminate the scrollwheel transaction.
michael@0:         nsIntPoint pt = GetScreenPoint(mouseEvent);
michael@0:         nsIntRect r = sTargetFrame->GetScreenRectExternal();
michael@0:         if (!r.Contains(pt)) {
michael@0:           EndTransaction();
michael@0:           return;
michael@0:         }
michael@0: 
michael@0:         // If the cursor is moving inside the frame, and it is less than
michael@0:         // ignoremovedelay milliseconds since the last scroll operation, ignore
michael@0:         // the mouse move; otherwise, record the current mouse move time to be
michael@0:         // checked later
michael@0:         if (!sMouseMoved && OutOfTime(sTime, GetIgnoreMoveDelayTime())) {
michael@0:           sMouseMoved = PR_IntervalToMilliseconds(PR_IntervalNow());
michael@0:         }
michael@0:       }
michael@0:       return;
michael@0:     }
michael@0:     case NS_KEY_PRESS:
michael@0:     case NS_KEY_UP:
michael@0:     case NS_KEY_DOWN:
michael@0:     case NS_MOUSE_BUTTON_UP:
michael@0:     case NS_MOUSE_BUTTON_DOWN:
michael@0:     case NS_MOUSE_DOUBLECLICK:
michael@0:     case NS_MOUSE_CLICK:
michael@0:     case NS_CONTEXTMENU:
michael@0:     case NS_DRAGDROP_DROP:
michael@0:       EndTransaction();
michael@0:       return;
michael@0:   }
michael@0: }
michael@0: 
michael@0: /* static */ void
michael@0: WheelTransaction::Shutdown()
michael@0: {
michael@0:   NS_IF_RELEASE(sTimer);
michael@0: }
michael@0: 
michael@0: /* static */ void
michael@0: WheelTransaction::OnFailToScrollTarget()
michael@0: {
michael@0:   NS_PRECONDITION(sTargetFrame, "We don't have mouse scrolling transaction");
michael@0: 
michael@0:   if (Preferences::GetBool("test.mousescroll", false)) {
michael@0:     // This event is used for automated tests, see bug 442774.
michael@0:     nsContentUtils::DispatchTrustedEvent(
michael@0:                       sTargetFrame->GetContent()->OwnerDoc(),
michael@0:                       sTargetFrame->GetContent(),
michael@0:                       NS_LITERAL_STRING("MozMouseScrollFailed"),
michael@0:                       true, true);
michael@0:   }
michael@0:   // The target frame might be destroyed in the event handler, at that time,
michael@0:   // we need to finish the current transaction
michael@0:   if (!sTargetFrame) {
michael@0:     EndTransaction();
michael@0:   }
michael@0: }
michael@0: 
michael@0: /* static */ void
michael@0: WheelTransaction::OnTimeout(nsITimer* aTimer, void* aClosure)
michael@0: {
michael@0:   if (!sTargetFrame) {
michael@0:     // The transaction target was destroyed already
michael@0:     EndTransaction();
michael@0:     return;
michael@0:   }
michael@0:   // Store the sTargetFrame, the variable becomes null in EndTransaction.
michael@0:   nsIFrame* frame = sTargetFrame;
michael@0:   // We need to finish current transaction before DOM event firing. Because
michael@0:   // the next DOM event might create strange situation for us.
michael@0:   MayEndTransaction();
michael@0: 
michael@0:   if (Preferences::GetBool("test.mousescroll", false)) {
michael@0:     // This event is used for automated tests, see bug 442774.
michael@0:     nsContentUtils::DispatchTrustedEvent(
michael@0:                       frame->GetContent()->OwnerDoc(),
michael@0:                       frame->GetContent(),
michael@0:                       NS_LITERAL_STRING("MozMouseScrollTransactionTimeout"),
michael@0:                       true, true);
michael@0:   }
michael@0: }
michael@0: 
michael@0: /* static */ void
michael@0: WheelTransaction::SetTimeout()
michael@0: {
michael@0:   if (!sTimer) {
michael@0:     nsCOMPtr<nsITimer> timer = do_CreateInstance(NS_TIMER_CONTRACTID);
michael@0:     if (!timer) {
michael@0:       return;
michael@0:     }
michael@0:     timer.swap(sTimer);
michael@0:   }
michael@0:   sTimer->Cancel();
michael@0:   DebugOnly<nsresult> rv =
michael@0:     sTimer->InitWithFuncCallback(OnTimeout, nullptr, GetTimeoutTime(),
michael@0:                                  nsITimer::TYPE_ONE_SHOT);
michael@0:   NS_WARN_IF_FALSE(NS_SUCCEEDED(rv), "nsITimer::InitWithFuncCallback failed");
michael@0: }
michael@0: 
michael@0: /* static */ nsIntPoint
michael@0: WheelTransaction::GetScreenPoint(WidgetGUIEvent* aEvent)
michael@0: {
michael@0:   NS_ASSERTION(aEvent, "aEvent is null");
michael@0:   NS_ASSERTION(aEvent->widget, "aEvent-widget is null");
michael@0:   return LayoutDeviceIntPoint::ToUntyped(aEvent->refPoint) +
michael@0:            aEvent->widget->WidgetToScreenOffset();
michael@0: }
michael@0: 
michael@0: /* static */ uint32_t
michael@0: WheelTransaction::GetTimeoutTime()
michael@0: {
michael@0:   return Preferences::GetUint("mousewheel.transaction.timeout", 1500);
michael@0: }
michael@0: 
michael@0: /* static */ uint32_t
michael@0: WheelTransaction::GetIgnoreMoveDelayTime()
michael@0: {
michael@0:   return Preferences::GetUint("mousewheel.transaction.ignoremovedelay", 100);
michael@0: }
michael@0: 
michael@0: /* static */ DeltaValues
michael@0: WheelTransaction::AccelerateWheelDelta(WidgetWheelEvent* aEvent,
michael@0:                                        bool aAllowScrollSpeedOverride)
michael@0: {
michael@0:   DeltaValues result(aEvent);
michael@0: 
michael@0:   // Don't accelerate the delta values if the event isn't line scrolling.
michael@0:   if (aEvent->deltaMode != nsIDOMWheelEvent::DOM_DELTA_LINE) {
michael@0:     return result;
michael@0:   }
michael@0: 
michael@0:   if (aAllowScrollSpeedOverride) {
michael@0:     result = OverrideSystemScrollSpeed(aEvent);
michael@0:   }
michael@0: 
michael@0:   // Accelerate by the sScrollSeriesCounter
michael@0:   int32_t start = GetAccelerationStart();
michael@0:   if (start >= 0 && sScrollSeriesCounter >= start) {
michael@0:     int32_t factor = GetAccelerationFactor();
michael@0:     if (factor > 0) {
michael@0:       result.deltaX = ComputeAcceleratedWheelDelta(result.deltaX, factor);
michael@0:       result.deltaY = ComputeAcceleratedWheelDelta(result.deltaY, factor);
michael@0:     }
michael@0:   }
michael@0: 
michael@0:   return result;
michael@0: }
michael@0: 
michael@0: /* static */ double
michael@0: WheelTransaction::ComputeAcceleratedWheelDelta(double aDelta,
michael@0:                                                int32_t aFactor)
michael@0: {
michael@0:   if (aDelta == 0.0) {
michael@0:     return 0;
michael@0:   }
michael@0: 
michael@0:   return (aDelta * sScrollSeriesCounter * (double)aFactor / 10);
michael@0: }
michael@0: 
michael@0: /* static */ int32_t
michael@0: WheelTransaction::GetAccelerationStart()
michael@0: {
michael@0:   return Preferences::GetInt("mousewheel.acceleration.start", -1);
michael@0: }
michael@0: 
michael@0: /* static */ int32_t
michael@0: WheelTransaction::GetAccelerationFactor()
michael@0: {
michael@0:   return Preferences::GetInt("mousewheel.acceleration.factor", -1);
michael@0: }
michael@0: 
michael@0: /* static */ DeltaValues
michael@0: WheelTransaction::OverrideSystemScrollSpeed(WidgetWheelEvent* aEvent)
michael@0: {
michael@0:   MOZ_ASSERT(sTargetFrame, "We don't have mouse scrolling transaction");
michael@0:   MOZ_ASSERT(aEvent->deltaMode == nsIDOMWheelEvent::DOM_DELTA_LINE);
michael@0: 
michael@0:   // If the event doesn't scroll to both X and Y, we don't need to do anything
michael@0:   // here.
michael@0:   if (!aEvent->deltaX && !aEvent->deltaY) {
michael@0:     return DeltaValues(aEvent);
michael@0:   }
michael@0: 
michael@0:   // We shouldn't override the scrolling speed on non root scroll frame.
michael@0:   if (sTargetFrame !=
michael@0:         sTargetFrame->PresContext()->PresShell()->GetRootScrollFrame()) {
michael@0:     return DeltaValues(aEvent);
michael@0:   }
michael@0: 
michael@0:   // Compute the overridden speed to nsIWidget.  The widget can check the
michael@0:   // conditions (e.g., checking the prefs, and also whether the user customized
michael@0:   // the system settings of the mouse wheel scrolling or not), and can limit
michael@0:   // the speed for preventing the unexpected high speed scrolling.
michael@0:   nsCOMPtr<nsIWidget> widget(sTargetFrame->GetNearestWidget());
michael@0:   NS_ENSURE_TRUE(widget, DeltaValues(aEvent));
michael@0:   DeltaValues overriddenDeltaValues(0.0, 0.0);
michael@0:   nsresult rv =
michael@0:     widget->OverrideSystemMouseScrollSpeed(aEvent->deltaX, aEvent->deltaY,
michael@0:                                            overriddenDeltaValues.deltaX,
michael@0:                                            overriddenDeltaValues.deltaY);
michael@0:   return NS_FAILED(rv) ? DeltaValues(aEvent) : overriddenDeltaValues;
michael@0: }
michael@0: 
michael@0: /******************************************************************/
michael@0: /* mozilla::ScrollbarsForWheel                                    */
michael@0: /******************************************************************/
michael@0: 
michael@0: const DeltaValues ScrollbarsForWheel::directions[kNumberOfTargets] = {
michael@0:   DeltaValues(-1, 0), DeltaValues(+1, 0), DeltaValues(0, -1), DeltaValues(0, +1)
michael@0: };
michael@0: 
michael@0: nsWeakFrame ScrollbarsForWheel::sActiveOwner = nullptr;
michael@0: nsWeakFrame ScrollbarsForWheel::sActivatedScrollTargets[kNumberOfTargets] = {
michael@0:   nullptr, nullptr, nullptr, nullptr
michael@0: };
michael@0: 
michael@0: bool ScrollbarsForWheel::sHadWheelStart = false;
michael@0: bool ScrollbarsForWheel::sOwnWheelTransaction = false;
michael@0: 
michael@0: /* static */ void
michael@0: ScrollbarsForWheel::PrepareToScrollText(EventStateManager* aESM,
michael@0:                                         nsIFrame* aTargetFrame,
michael@0:                                         WidgetWheelEvent* aEvent)
michael@0: {
michael@0:   if (aEvent->message == NS_WHEEL_START) {
michael@0:     WheelTransaction::OwnScrollbars(false);
michael@0:     if (!IsActive()) {
michael@0:       TemporarilyActivateAllPossibleScrollTargets(aESM, aTargetFrame, aEvent);
michael@0:       sHadWheelStart = true;
michael@0:     }
michael@0:   } else {
michael@0:     DeactivateAllTemporarilyActivatedScrollTargets();
michael@0:   }
michael@0: }
michael@0: 
michael@0: /* static */ void
michael@0: ScrollbarsForWheel::SetActiveScrollTarget(nsIScrollableFrame* aScrollTarget)
michael@0: {
michael@0:   if (!sHadWheelStart) {
michael@0:     return;
michael@0:   }
michael@0:   nsIScrollbarOwner* scrollbarOwner = do_QueryFrame(aScrollTarget);
michael@0:   if (!scrollbarOwner) {
michael@0:     return;
michael@0:   }
michael@0:   sHadWheelStart = false;
michael@0:   sActiveOwner = do_QueryFrame(aScrollTarget);
michael@0:   scrollbarOwner->ScrollbarActivityStarted();
michael@0: }
michael@0: 
michael@0: /* static */ void
michael@0: ScrollbarsForWheel::MayInactivate()
michael@0: {
michael@0:   if (!sOwnWheelTransaction && WheelTransaction::GetTargetFrame()) {
michael@0:     WheelTransaction::OwnScrollbars(true);
michael@0:   } else {
michael@0:     Inactivate();
michael@0:   }
michael@0: }
michael@0: 
michael@0: /* static */ void
michael@0: ScrollbarsForWheel::Inactivate()
michael@0: {
michael@0:   nsIScrollbarOwner* scrollbarOwner = do_QueryFrame(sActiveOwner);
michael@0:   if (scrollbarOwner) {
michael@0:     scrollbarOwner->ScrollbarActivityStopped();
michael@0:   }
michael@0:   sActiveOwner = nullptr;
michael@0:   DeactivateAllTemporarilyActivatedScrollTargets();
michael@0:   if (sOwnWheelTransaction) {
michael@0:     sOwnWheelTransaction = false;
michael@0:     WheelTransaction::OwnScrollbars(false);
michael@0:     WheelTransaction::EndTransaction();
michael@0:   }
michael@0: }
michael@0: 
michael@0: /* static */ bool
michael@0: ScrollbarsForWheel::IsActive()
michael@0: {
michael@0:   if (sActiveOwner) {
michael@0:     return true;
michael@0:   }
michael@0:   for (size_t i = 0; i < kNumberOfTargets; ++i) {
michael@0:     if (sActivatedScrollTargets[i]) {
michael@0:       return true;
michael@0:     }
michael@0:   }
michael@0:   return false;
michael@0: }
michael@0: 
michael@0: /* static */ void
michael@0: ScrollbarsForWheel::OwnWheelTransaction(bool aOwn)
michael@0: {
michael@0:   sOwnWheelTransaction = aOwn;
michael@0: }
michael@0: 
michael@0: /* static */ void
michael@0: ScrollbarsForWheel::TemporarilyActivateAllPossibleScrollTargets(
michael@0:                       EventStateManager* aESM,
michael@0:                       nsIFrame* aTargetFrame,
michael@0:                       WidgetWheelEvent* aEvent)
michael@0: {
michael@0:   for (size_t i = 0; i < kNumberOfTargets; i++) {
michael@0:     const DeltaValues *dir = &directions[i];
michael@0:     nsWeakFrame* scrollTarget = &sActivatedScrollTargets[i];
michael@0:     MOZ_ASSERT(!*scrollTarget, "scroll target still temporarily activated!");
michael@0:     nsIScrollableFrame* target =
michael@0:       aESM->ComputeScrollTarget(aTargetFrame, dir->deltaX, dir->deltaY, aEvent,
michael@0:               EventStateManager::COMPUTE_DEFAULT_ACTION_TARGET);
michael@0:     nsIScrollbarOwner* scrollbarOwner = do_QueryFrame(target);
michael@0:     if (scrollbarOwner) {
michael@0:       nsIFrame* targetFrame = do_QueryFrame(target);
michael@0:       *scrollTarget = targetFrame;
michael@0:       scrollbarOwner->ScrollbarActivityStarted();
michael@0:     }
michael@0:   }
michael@0: }
michael@0: 
michael@0: /* static */ void
michael@0: ScrollbarsForWheel::DeactivateAllTemporarilyActivatedScrollTargets()
michael@0: {
michael@0:   for (size_t i = 0; i < kNumberOfTargets; i++) {
michael@0:     nsWeakFrame* scrollTarget = &sActivatedScrollTargets[i];
michael@0:     if (*scrollTarget) {
michael@0:       nsIScrollbarOwner* scrollbarOwner = do_QueryFrame(*scrollTarget);
michael@0:       if (scrollbarOwner) {
michael@0:         scrollbarOwner->ScrollbarActivityStopped();
michael@0:       }
michael@0:       *scrollTarget = nullptr;
michael@0:     }
michael@0:   }
michael@0: }
michael@0: 
michael@0: } // namespace mozilla